The present disclosure relates to the processing of substrates in plasma process equipment. In particular, it provides a method to control plasma etching of layers comprising oxides.
The use of plasma systems for the processing of substrates has long been known. For example, plasma processing of semiconductor wafers is well known. One well known use of plasma processing is for etching of substrates. Plasma etching presents numerous technical challenges. Further as geometries for structures and layers on substrates continue to shrink, tradeoffs between etch selectivity, profile, aspect ratio dependent etching, uniformity, etc. become more difficult to manage. In order to achieve desired process performance, variable settings of the plasma processing equipment can be adjusted to change the plasma properties. These settings include, but are not limited to gas flow rates, gas pressure, electrical power for the plasma excitation, bias voltages, etc., all as is known in the art. However, as geometries continue to shrink it has been found that sufficient control of ion energy, ion flux, radical flux, etc. that results from the settings of the plasma processing equipment is not satisfactory to achieve the desired etch results.
One technique to improve plasma etching has been to utilize atomic layer etch (ALE) plasma processes. ALE processes are general known to involve processes which remove thin layers sequentially through one or more self-limiting reactions. Thus, ALE processes offer improved performance by decoupling the etch process into sequential steps of surface modification and removal of the modified surface, thereby allowing the segregation of the roles of radical flux and ion flux and energy. Such processes often include multiple cyclic series of layer modification and etch steps. The modification step may modify the exposed surfaces and the etch step may selectively remove the modified layer. Thus, a series of self-limiting reactions may occur. As used herein, an ALE process may also include quasi-ALE processes. In such processes, a series of modification and etch step cycles may still be used, however, the removal step may not be purely self-limiting as after removal of the modified layer, the etch substantially slows down, though it may not completely stop. In either case, the ALE based processes include a cyclic series of modification and etch steps.
It would be desirable to provide an improved ALE process. More specifically, it would be desirable to provide an improved ALE process for etching of oxides.